An important and frequently required diagnostic analysis, such as may be performed in clinical or laboratory medical practice, is the automated chemical analysis of biological samples, and in particular biological samples containing whole cells or cellular debris, such as whole blood, plasma or serum, or other biological fluids wherein the term fluid includes both liquids and gases. The analysis of biological samples containing cells or cellular debris saves valuable time in reaching a diagnosis and treatment by eliminating the separation step, which can be critical in an emergency situation, and reduces the cost of each analysis.
A major problem in the automated chemical analysis of samples containing whole cells or cellular debris, however, is the delivery of the samples from a sample container, such as a hypodermic tube, test tube or other sample container, and into the analysis apparatus. Biological samples, and in particular those containing cellular materials, have a tendency to leave films containing proteins and other biological molecules on the surfaces of the analysis apparatus. As a result, each of successive samples introduced into the analysis apparatus can simultaneously pick up constituents left on the surfaces from previous samples and deposit new constituents, so that a sample can be contaminated by one or more previous samples. This problem is particularly acute given the sizes of the samples customarily used in such analyzers, which are typically in the range of micro-liters.
These residual films tend to accumulate over time, so that the problem increases as the number of samples increases, and the interaction between a given sample and the residual films from previous samples in unpredictable, depending upon the constituents of the samples and the composition of the residual films.
Methods for dealing with this problem as regards the interior surfaces of an analysis apparatus have long been available and generally involve regular washing or flushing of the interior passages and chambers of the apparatus through which the biological samples pass. A typical analysis apparatus will normally use the pumps, tubing and passages used to move the samples through the device to also move the cleaning solutions through the device, thereby insuring that all internal surfaces, passages and chambers that come in contact with the samples also come in contact with the cleaning solutions. These cleaning solutions range from mild to aggressive, usually containing strong alkaline constituents, such as bleach, or enzymatically active constituents, such as proteases. For this reason, many automated analysis devices are provided with containers, either located within the apparatus or outside the apparatus itself, for storing cleaning solutions and the waste products resulting from cleaning operations.
These cleaning methods are confined to the interior surfaces of the analysis apparatus, that is, the surfaces of the passages and chambers through which the samples and reagents flow in passing from the sample entry point to the analysis sensors and the surfaces of the analysis sensors that are contacted by the samples. It will be noted, however, that the methods of the prior art for cleaning even the interior surfaces of an analysis apparatus are often inadequate to prevent interaction between a sample and the residue or residual films from previous samples and there is frequently contamination between samples and calibration reagents. In particular, the interior fluid paths of the analysis apparatus of the prior art frequently include "dead" spaces or voids that trap portions of the samples and fluids flowing therethrough and such "dead" spaces and voids are difficult to flush out or clean, so that the residues or films trapped in such areas may in turn contaminate subsequent samples. Such voids and "dead" spaces frequently occur, for example, in the corners of sharp bends in the fluid paths, in the corners formed where the fluid path changes dimensions and at sliding joints between sections of the fluid path. In addition, it is common in analysis apparatus of the prior art that the fluids pass through various moving parts in the path to the analysis sensors and such moving parts, such as sliding joints, valves and pumps, frequently contain voids and "dead" spaces that trap residues or residual films that may contaminate other fluids subsequently flowing through the apparatus.
Further, it is apparent that the samples also contact the exterior surfaces of the apparatus, in particular at or around the sample entry point where the samples first enter an analysis device, such as at the input to an aspirating probe through which the samples are drawn into the apparatus. Because these surfaces are not interior to the device, and are therefore not part of the cleaning solution path within the device, the films can build up on these surfaces in a relatively unhindered manner.
The buildup of films and deposits on the exterior surfaces of an analysis apparatus, for example, at the sample entry point such as an aspiration probe, have been usually handled in the prior art by having the user manually wipe the contaminated surfaces. This method, however, is unsatisfactory for many reasons. For example, not only does the manual cleaning of the apparatus impose an additional task on an already too busy user, but the user may forget to clean the sample entry as often as necessary, or at all, with resulting contamination of the samples. In addition, the user is undesirably exposed to biological hazards when manually cleaning the apparatus, such as puncture wounds from a contaminated aspiration probe and the sample residues themselves. The user must also safely dispose of the contaminated cleaning supplies, further adding to the cost and inconvenience of analyzing biological samples.
Another problem in the automated biological analysis apparatus of the prior art arises from the need to calibrate the analysis apparatus in order to validate the results of the sample analyses. In this regard, the cost of providing separate means for delivering the calibration samples, or calibrantes, and the samples to be analyzed into the apparatus can be unacceptable and, if the calibrante and analysis sample delivery paths are not substantially the same, the differences in the paths can introduce systematic errors in the analysis process as regards the calibrantes or the samples being analyzed, or both.
For these reasons, the means by which calibrantes are introduced to the analysis mechanism and sensors is generally the same as that used to introduce the samples to be analyzed and the calibrantes generally follow the same flow path as the samples. This, however, can result in cross-contamination between the calibrantes and the samples and this cross-contamination can be more critical than cross-contamination between samples. This problem is compounded where multiple calibrantes are necessary, as the means by which the calibrantes are introduced to the apparatus must include the capability of switching among the calibrantes without cross-contamination among the calibrantes or between the calibrantes and the samples to be analyzed. The problem is further compounded in that many current analyzers provide completely automatic calibration, so that the means by which the calibrantes are introduced are more complex while, at the same time, being less accessible for cleaning.
Still another problem in the automated biological analysis apparatus of the prior art arises because the biological samples to be analyzed may be provided in a variety of sample containers, such as Vacutainer tubes, syringes, capillary tubes of various sizes, and a variety of types and sizes of sample cups and beakers. While the sample entry point of the analysis apparatus should be capable of accepting samples directly from any of these containers, thereby providing users with the maximum flexibility as regards the acquisition and storage of samples, each different type of sample container places a different geometric constraint on the entry point and on the operations by which the samples are introduced into the analysis apparatus. This, in turn, has previously significantly increased the cost and complexity of the analysis apparatus and made the apparatus more complex for the user and, at times, very awkward for the user.
Yet another problem of the analysis apparatus of the prior art is in the valves used to select and route calibration and cleaning fluids, and perhaps sample fluids, into and through the analysis. In addition to the problems of the prior art discussed above, the design of such valves has generally conformed to traditional principles, using traditional materials such as metal or plastic for the body and moving parts of the valve and using traditional methods such as plastic or rubber seals, such as O-rings and washers, to prevent leakage from or into the valve passages. Such valves tend to be expensive to manufacture, require significant and frequent maintenance, and generally become unusable due to wear in a relative short time. In addition, and as discussed above, the traditional designs of such valves frequently include small voids or "dead areas", as described above, which trap films or residues of the calibration and cleaning fluids and samples flowing therethrough, so a one fluid or sample may frequently contaminate a subsequent fluid or sample.
Still another problem of the analysis devices of the prior art concerns the difficulty and complexity of the operations and actions required of a user of the apparatus, which may be regarded as "ease of use" issues. One group of such issued relates directly to the analysis of individual samples and concern the convenience with which a user may use the apparatus to analyze a sample. For example, and as discussed above, the user should be able to present samples to the apparatus from a variety of types of sample containers without the need for special adaptations or operations to switch from one type of container to another. In another aspect of this same issue, it has been described that the analysis devices of the prior art generally require a user to frequently manually clean the means by which samples and calibrantes are introduced into the device, which is an inconvenient and potentially hazardous operation that would preferably be eliminated.
In yet another aspect of ease of use of an analysis apparatus or device concerns what may be referred to as the "logistic" aspects of the apparatus, that is, its portability, the ease or difficulty of supplying the apparatus with reagents and cleaning or calibration fluids, and the ease or difficulty of adapting the apparatus to perform different tests or multiple tests at the same time or to adding new analysis sensors. It is preferable that the apparatus be modular to the greatest possible extent.
To illustrate, such analysis apparatus is generally provided with replaceable reservoirs, containing calibrants, reagents and cleaning fluid and the replaceable reservoirs are sometimes combined into a unit known as a reagent or fluids pack. For the case of blood gas analyzers, however, external tanks of calibrated gases are usually required in addition to the replaceable reagent pack. The elimination of external calibration gas tanks and the incorporation of the calibration gases into the calibrant solutions within a modular, replaceable and self-contained reagent pack containing all reagents and calibrating solutions used in the analyses and calibrations, including the calibrants for gas sensors, is thereby advantageous. Not only would such a reagent pack be more convenient in that a reagent pack may simply be replaced as necessary, but the apparatus could be more portable.
This, however, presents certain problems in the design and construction of such reservoirs, or fluid packs, which are rarely or poorly met by the fluid packs of the prior art. Packs used to store, for example, calibration fluids used in association with the measurement of blood gases contain carefully calculated concentrations of gases. These containers must therefore prevent the escape or absorption of gases for extended periods, including an unknown shelf storage time and travel time. This requirement is even more stringent when the packs are required to be shipped under conditions, such as air freight, where the external atmospheric pressure may vary widely, as may the temperature. Another and related effect to be guarded against is the formation of gas bubbles in the containers since the escape of gases from solution will affect the calibrated concentration of gases in the fluid, even though the gases do not escape the container. Still another problem of the prior art arises from the methods used in the prior art to prevent the escape or absorption of gases from or into a fluid by providing a gas tight metal foil liner, such as aluminum foil. While such metal liners are of value in preventing or reducing the escape or absorption of gases from or into a fluid, the metal foil itself may chemically react with the fluid, thereby destroying or undesirably altering the characteristics of the fluid stored therein.
The present invention provides a solution to these and other problems of the prior art.